Chemical analysis of a test sample often involves the use of UV/visible radiation from 300 nm to 700 nm, to determine quantitatively the composition of biological fluids like serum. Reflectance or transmission density, or fluorescence measurements of the test element, can be used to calculate chemical concentrations thereby providing a more complete picture of a patient's condition.
In dry chemistry (as used herein, "dry chemistry" refers to tests wherein there are no liquid reagents stored for use, such tests being possible by test elements of the type described in U.S. Pat. No. 3,992,158, Nov. 16, 1976) blood analysis, a sample of blood serum, is added to a test element containing chemical reagents. After sufficient incubation time, a color change or fluorescence is detected by a radiometer. The following is a typical example of a colorimetric test for albumin: EQU Albumin+Boromcresol Green (BCG).fwdarw.BCG-Albumin (Complex) (Max. Abs. 630 nm)
where the BCG-Albumin complex, formed upon the interaction of albumin with the indicator bromocresol green (BCG), absorbs radiation and the absorption maximum is at 630 nm. The degree of radiation absorption can be monitored as a measure of the albumin concentration. The trend in this industry is toward smaller more compact instruments such that their use could be extended to smaller institutions and individual practices.
The prior art includes several types of light sources that can be used for making measurements in the 300 nm to 700 nm range such as tungsten halogen and pulsed xenon lamps. FIG. 10 shows a schematic of a typical arrangement for this type of measurement with the exception that, in the prior art, a tungsten lamp and cold mirror are used. In the present invention an upconversion light source is used which will be described later. Some of the problems associated with the prior art tungsten radiation sources are: their relatively low stability; short life; size; lack of compactness; and ruggedness. Furthermore, tungsten halogen lamps have relatively short lives, generate excessive heat, and have a low ratio of usable light to power in the UV-blue region of the spectrum. In addition, the output power or intensity decreases with time and with filament life.
These lamps, in general, are large and cumbersome and require frequent adjustments and replacement because of burned out filaments. In addition, these lamps preclude efforts to miniaturize such equipment and also pose a potential danger to operators and to the equipment itself because of the heat generated during their operation. The wavelengths produced may vary as a function of time with the aging of the lamps, and because the process involves Ar or halogen gases that have to be "ignited" in order to produce radiation, it is not possible to modulate these lamps at rates faster than what a mechanical shutter would provide.
With respect to xenon sources, although there is a high ratio of usable radiant energy with respect to power and heat generated, the measurement of that power is limited to a short time. High voltages and sudden surges of high current generate electrical noise that often interferes with other electronic subsystems.